The keystone in Allen's masterpiece triliogy.
Love and Death, Manhattan and Annie Hall have got to be his three greatest films.
Love and Death is hillarious and has so many subtle jokes but also has a lot of commentary on philosophy and love. I mean, if ever a comedy could be outrageous and intelligent, this is it.
Manhattan is the best depiction of New York City in the history of cinema and very funny and if you had only one Woody Allen film I would say Manhattan because it covers the bases the best. It isn't as personal but in a good way.
Annie Hall is his most personal and really deals with relationships. The characters are the most developed of any of his films and Allen is actually able to achieve a sense of time, a sense that these people found a bond and lost it.
These three movies are three of my favorites of all time. I don't like repeating directors so the Number 2 spot of all time films is reserved for whichever of these films. I usually go with Love and Death.